1. Field of the Invention
The present invention relates to a printing apparatus and roll paper conveyance control method and, particularly, to a printing apparatus which stabilizes, for example, a variation of back-tension in conveyance of roll paper by a conveyance roller, and a roll paper conveyance control method in the apparatus.
2. Description of the Related Art
Torque control of a DC motor in a general circuit configuration is feedback control of compensating for a current value to be applied to the motor by adjusting a voltage applied to a driving circuit so as to supply a desired current based on the result of detection by a detection unit which detects a current value or voltage value applied to the motor.
As torque control of a DC motor having this configuration, for example, Japanese Patent Laid-Open No. 8-130893 discloses a method of estimating a rotational position and rotational speed by a current sensor and voltage sensor, and performing control based on the estimated values. The estimated values of the rotational position and rotational speed at this time are compared with those of a rotational position and rotational speed at the previous time. If the comparison result reveals that the change exceeds a predetermined reference change amount, it is determined that noise has been mixed in the sensors and an error has occurred. Then, the estimated values at this time are replaced with alternative values, thereby preventing degradation of operation stability caused by superimposition of noise.
However, the conventional DC motor control circuit has the following problems.
For example, in Japanese Patent Laid-Open No. 8-130893, the moving average of an average load torque is used to calculate the estimated values of a rotational position and rotational speed. When the moving average period is short and large noise is mixed in the feedback control system, no accurate control can be achieved because the influence of the noise on the moving average value is serious. When the moving average period is long, noise tolerability is improved, but traceability to a small variation is impaired.
Since a complicated algorithm is used to calculate an estimated value, an error occurs in calculation by the CPU and the circuit scale is expanded.